Blood treatment method adapted to at least partially eliminate the carbon dioxide content and related device

ABSTRACT

A blood treatment method is described that is adapted to at least partially eliminate the carbon dioxide content of the type comprising a step of drawing a blood flow. Advantageously according to the invention, the method further comprises the steps of: acidifying the blood flow with transformation of the related blood bicarbonate content into gaseous carbon dioxide; and eliminating the gaseous carbon dioxide content by means of a pressure gradient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/599,254, filed Nov. 6, 2009 (with an effective filing date of Feb. 4,2010), which is a national phase of PCT/EP2008/003661, filed May 7,2008, which claims priority to Italian Patent Application No.MI2007A000913, filed May 7, 2007. The entire contents of theseapplications are incorporated herein by reference.

FIELD OF APPLICATION

The present application refers to a blood treatment method adapted to atleast partially eliminate the carbon dioxide content.

The invention also refers to a blood treatment device.

PRIOR ART

As it is well known, the lungs are very elastic organs, situated in thethoracic cavity, capable of expanding and contracting in order tointroduce and expel air. In particular, each lung is formed by alveolialso called respiratory cells, since the gas exchange between the bloodand the breathed air occurs therein, the related surface beingvascularized by a great number of capillaries coming from the pulmonaryartery.

The air that is breathed, through the respiratory pathways, then arrivesat the pulmonary alveoli. Here the oxygen (O₂) passes via diffusion intothe capillaries, binding itself to the haemoglobin, through thecirculatory system, arriving at all body tissues. One of the finalproducts of the chemical reactions occurring in the tissues, i.e. thecarbon dioxide (CO₂), is meanwhile collected by the circulating bloodand transported to the pulmonary capillaries, where it diffuses in thealveoli and then it is expelled during expiration, always through therespiratory pathways.

The body metabolism, in substance, consumes oxygen and produces carbondioxide. Oxygen and carbon dioxide are then exchanged with theatmospheric air by means of the ventilation mechanism achieved by thelungs, where the blood is loaded with oxygen and gives up carbondioxide.

These processes can be slowed to a fraction of the normal resting level(considered to be the reference level), e.g. by hypothermia, oraccelerated up to 20 times the resting level when the metabolismincreases, such as in the case of fever, hyperthermia or physicalexertion.

The amount of air inserted and emitted in the lungs during a normalrespiratory act is about 500 cm³, but it can considerably increase.

Physiological mechanisms coupled and balanced by chemical buffer systemsalways maintain the oxygen/carbon dioxide exchange system in the lungsin equilibrium.

In numerous pathological conditions, however, the elimination of carbondioxide through the lungs is altered, made difficult or in any caseinterferes with other physiological and/or therapeutic processes (suchas artificial mechanical ventilation).

In such cases, it is known to employ a blood processing organ, inparticular known as artificial lung, that can be utilized to assist adeficiency of the natural organ both for brief time periods orpermanently, or even to substitute the entire pulmonary exchangefunction, if for example the natural organ is completely insufficient,or if, still healthy, it must be stopped for a limited time period, forexample due to a surgical operation.

Currently, artificial lungs are achieved by means of relatively largedevices, and cannot be placed in the anatomic site of the natural lungs.In particular, the venous blood is deviated from its normal coursethrough the central veins and is redirected by means of catheters andtubes into an extracorporeal circuit comprising the artificial lung, soto be finally returned—by means of a pump—to the arterial system, thusavoiding heart and lungs.

The interruption of the pulmonary circulation and the use of anartificial lung for surgical applications is often indicated as anextracorporeal circulation, since in operating rooms, the device for thegas exchange and the pump which makes the blood circulate are placedoutside the body.

In particular, the venous blood, excluded from the lung circuit, comesto be artificially oxygenated by means of a gas exchanger, in particularan oxygenator.

The oxygenator is only a part of a great veno-arterial-cardiopulmonarycircuit that takes the name of heart-lung machine. In particular, insuch a machine, all of the venous blood, which returns towards the rightatrium of the heart, is collected in an extracorporeal circuit, pumpedinto an oxygenator from which it is conveyed into the arterial circuit,thus avoiding the heart and the pulmonary circuit.

During this process, the blood is heparinised in order to avoid theformation of thrombi and its temperature is lowered several degrees inorder to reduce oxygen consumption by the main organs, while oxygen, ora mixture of gas rich in oxygen, flows from a moderately pressurizedsource in a continuous manner and without recirculation.

The main problem encountered in making an oxygenator that acts as anartificial lung is the creation of a large surface for gas-bloodexchange. This problem is resolved in the prior art using a membraneoxygenator, by making blood and gas flow along opposite faces of a gaspermeable membrane.

The currently available equipment thus operates on the carbon dioxideamount dissolved as gas in the blood, which in reality is a limitedportion of the total carbon dioxide content of the blood.

In fact, in all membrane exchangers, the gases are moved from the higherpartial pressure compartment towards the lower one. In the case ofcarbon dioxide, this is moved from the side of the biological liquids(blood, plasma, ultrafiltrate, etc.) towards that of the ventilationfluid, moved by a relatively small pressure gradient. Only very rarelyand in seriously pathological conditions, the body carbon dioxidepressure naturally exceeds 80 mmHg, while the carbon dioxide pressure ofthe ventilation fluid can never be less than 0 mmHg. There is thereforea pressure gradient physiologically limited to a value equal to 5-10% ofthe atmospheric pressure.

It is therefore necessary to treat a large amount of blood in order toeliminate a carbon dioxide amount such as to maintain constant its levelin the blood, notwithstanding the continuous production by the bodymetabolism. In particular, it is known that a man of medium build of 70Kg produces carbon dioxide in an amount equal to about 10 mMol/min: thisis therefore the amount that a membrane oxygenator must eliminate, inpractice necessitating the treatment of about 1.5-2.5 liters/min ofblood. This is the objective in the case of the so-called “Total CO2Removal”, with the possibility of a complete apnoea for an indeterminatetime, i.e. total substitution of the natural respiratory function.

The involved amounts of blood to be treated require the use of machinesand procedures that are particularly invasive, which limit their use toheart surgery operations or to extremely serious situations, as a lastresort for preventing death.

Moreover, the patient must be connected to such machines at importantvessels of the body, by means of semi-permanent implants that cannot becompared to the cannulas currently used for example in the case ofdialysis, with a considerable risk of major complications, even death,for the patient. Finally, the high volume of treated blood increases therisks of damage to its corpuscular parts, obliging the patient to followappropriate support therapies.

The technical problem underlying the present invention is that ofproviding a treatment method of the blood, and related device, thatpermits reducing the carbon dioxide content of the treated blood,reducing the blood flows and volumes necessary for obtaining a partialor total substitution of the natural ventilation mechanism, in such amanner overcoming the limitations and drawbacks that still limit thedevices made according to the prior art.

SUMMARY OF THE INVENTION

The solution idea underlying the present invention is that of acting onthe carbon dioxide portion in the blood in bicarbonate form, suchportion being much greater than the one dissolved as gas.

On the basis of such solution idea, the technical problem is solved by atreatment method of the blood adapted to at least partially eliminatefrom it the carbon dioxide content of the type comprising a step ofdrawing a blood flow and characterized in that it further comprises thesteps of:

acidifying said blood flow with transformation of the related bloodbicarbonate content into gaseous carbon dioxide; and

eliminating said gaseous carbon dioxide content by means of a pressuregradient. An extracorporeal blood treatment is thus obtained.

Advantageously, according to the invention, said acidifying stepcomprises a step of inserting an acid load.

Further advantageously, the method also comprises a step of removingsaid acid load from said acidified blood flow with the obtainment of atreated blood flow, as well as a step of ventilating simultaneous withsaid acidification step and a possible step of oxygenating said bloodflow through an artificial membrane lung.

Appropriately, said insertion step of said acid load provides for aninflow of a mixture of organic and inorganic acids in variousproportions and total amount.

Advantageously according to the invention, the treatment method of theblood can comprise a preliminary step of filtering said blood flow, saidacidification step being made on an ultrafiltrate thus obtained.

Further advantageously, the method comprises a recirculation step ofsaid blood flow in a feedback path, with insertion of a treated bloodportion to said blood flow immediately following said acidificationstep. The method according to the invention also comprises, in said stepof removing said acid load, a step of hydroelectrolytic rebalancing,achieved in one of the following methods:

direct haemodialysis of said treated blood flow;

filtration of said treated blood flow, with obtainment of anultrafiltrate and elimination of an ultrafiltrate amount such tocompensate for said inserted acid load, with subsequent infusion of abasic load amount;

balancing, via dialysis or electrodialysis, of an ultrafiltrate possiblywith a batch liquid subjected to desalination, with a subsequentinfusion of a basic load amount if required;

balancing of an ultrafiltrate via electrodialysis or diffusion dialysiswith net removal of the added acid load and possible reutilization ofthe same for blood acidification.

The problem is also solved by a blood treatment device adapted to atleast partially eliminate the carbon dioxide content of the typecomprising at least one inlet terminal for inflow of a blood flow and anoutlet terminal for outflow a treated blood flow characterized in thatit comprises at least one acidification stage and one gas exchangerinserted, in series with each other, between the inlet and outletterminals, said gas exchanger eliminating the gaseous carbon dioxidecontent of said venous blood flow acidified by said acidification stage.

Advantageously according to the invention, said acidification stage isadapted to insert an acid load in said venous blood flow with obtainmentof an acidified blood flow that is inserted into said gas exchanger,which ventilates it.

Further advantageously according to the invention, a deacidificationstage is inserted downstream of said gas exchanger, in order to supplysaid treated blood flow at said outlet terminal.

Suitably, said gas exchanger is a membrane oxygenator adapted toeliminate, via pressure gradient, the gaseous carbon dioxide contentfrom said acidified gas flow and possibly to oxygenate it, giving riseto a decarbonised and possibly oxygenated blood flow, still acidified,sent to said deacidification stage.

Further advantageously according to the invention, said deacidificationstage is adapted to remove the acid load by means of elimination ofanions with inflow of a basic load to said decarbonised and possiblyoxygenated blood flow with obtainment of a treated blood flow, suppliedto said outlet terminal.

The device according to the invention further comprises a recirculationblock adapted to draw, in a feedback path, a portion of saiddecarbonated blood downstream of said gas exchanger and to mix it withsaid acidified blood flow in order to lower the blood pH upstream ofsaid gas exchanger.

In an advantageous alternative embodiment, the device further comprisesa haemofilter for producing an ultrafiltrate, appropriately connectedupstream of said acidification stage or inserted between saidacidification stage and said gas exchanger or also connected downstreamof said gas exchanger.

Said haemofilter is also advantageously inserted in said feedback pathwith said recirculation block.

The features and advantages of the method and device of blood treatmentaccording to the invention will be clearer from the followingdescription, made hereinbelow, of an embodiment thereof given asindicative and non-limiting example with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In such drawings:

FIG. 1 schematically shows a blood treatment device adapted to implementthe method according to the invention;

FIG. 2 schematically shows a first alternative embodiment of the bloodtreatment device according to the present invention;

FIG. 3 schematically shows a second alternative embodiment of the bloodtreatment device according to the present invention; and

FIG. 4 schematically shows a third alternative embodiment of the bloodtreatment device according to the present invention.

DETAILED DESCRIPTION

First of all, it is opportune to underline the fact that the presentinvention primarily arises from the consideration that carbon dioxide istransported in the blood according to two principal mechanisms:

dissolved as a gas; as

in a bicarbonate ion form

and from the fact that the carbon dioxide portion present as abicarbonate ion is much greater than the amount dissolved as a gas.

Starting from such considerations, advantageously according to theinvention, a blood treatment method is proposed for eliminating thecarbon dioxide by means of a conversion of its portion present as abicarbonate ion, indicated below as blood bicarbonate.

In particular, advantageously according to the invention, the methodcomprises a reaction step of such blood bicarbonate and itstransformation into gaseous carbon dioxide, which is then eliminated bymeans of a simple pressure gradient.

It should be recalled that a similar mechanism is used in naturalventilation, i.e. by the lungs, where an enzyme, in particular carbonanhydrase, permits the reaction of the blood bicarbonate and itstransformation into gas, normally a very slow reaction.

It is also underlined that such chemical reaction with transformation ofthe blood bicarbonate into gaseous carbon dioxide liberates an amount ofgas that is absolutely within the capacity of a normal membraneoxygenator, whose effectiveness is limited in known equipment only bythe reduced carbon dioxide amount already present in gaseous form.

Furthermore, it is underlined that the partial pressure of carbondioxide at the time of the transformation of the blood bicarbonate intogaseous carbon dioxide increases up to ten times, thus proportionatelyincreasing the carbon dioxide elimination capacity of the employedmembrane oxygenator.

More in detail, the blood treatment method according to the inventioncomprises the following fundamental steps:

acidifying the blood with transformation of the blood bicarbonate intogaseous carbon dioxide; and

eliminating the gaseous carbon dioxide content.

An extracorporeal blood treatment is thus obtained.

Advantageously according to the invention, the blood acidification stepcomprises a simultaneous ventilation of the same. During suchventilation step, an oxygenation step of the blood flow is alsoprovided.

In addition, the method comprises a final step for removing the acidload remaining in the blood. It is thus possible to reinsert the treatedblood (in particular cleaned of its carbon dioxide content, oxygenatedand purified of the acid load) in the patient.

Advantageously according to the invention, the step of acidifying theblood comprises a step for inserting an acid load (in particular ananionic load) in the blood, more in particular a mixture of an inorganicacid in various proportions and total amount, such as hydrochloric acidHCl, and organic acids, such as pyruvic acid, citric acid and lacticacid (already normally existing and metabolized in the organism). Morein detail, one such acid mixture is inserted in an amount normally inthe range of 0-10 mMol/min in the blood as drawn from a patient,typically venous blood that returns towards the right atrium of theheart loaded with carbon dioxide and poor in oxygen.

In such a manner, for a blood flow for example of 400 ml/min that, aswill be clear in the following description, is sufficient for ensuringthe desired elimination of carbon dioxide for a total substitution ofthe natural ventilation, a maximum addition (under normal conditions) ofabout 25 mMol/liter of acid load is considered.

It can be immediately verified that the addition of such maximum acidload converts nearly all of the blood bicarbonate, i.e. the bicarbonateion contained in the blood bound to the water (equal to about 25mMol/litro) into gaseous carbon dioxide or carbonic acid.

The partial pressure of gaseous carbon dioxide obtained by theabove-indicated reaction reaches values greater than 450 mmHg. It isopportune to emphasize the fact that, even in closed environments (i.e.non-ventilated environments), such pressure values are in any casesecure, since they do not lead to the formation of bubbles ormicro-bubbles.

It is also verified that, following the addition of the acid load in theabove-indicated proportions, the blood pH value or haematic pH would beas low as approximately 5.7, a very dangerous value for the survival ofthe red corpuscles and other blood cells. Advantageously according tothe invention, the ventilation step of the blood flow is thereforeprovided, in particular by using a membrane oxygenator, bringing thegaseous carbon dioxide pressure to values of 5-20 mmHg and the blood pHto nearly normal values.

Membrane oxygenator, thanks to the high partial pressure of the carbondioxide thus generated, in this manner nearly completely eliminates thegaseous carbon dioxide content of the acidified blood.

It should be noted that the acidification step of the blood or of theultrafiltrate raises considerably the carbon dioxide pressure, favouringits removal towards a gaseous phase at a lower carbon dioxide pressure,i.e. towards an employed ventilation gas.

Appropriately, the membrane oxygenator also achieves the desiredoxygenation step of the blood.

In a preferred embodiment of the invention, in order to avoid locallysharp drops of the blood pH as well as local accumulations of gaseouscarbon dioxide, the method comprises a preliminary step ofultrafiltration of the blood, with separation of its corpuscle part fromthe plasma or ultrafiltrate (as will be better explained in thefollowing description with reference to FIG. 2).

In such a case, the acidification step of the blood provides for theaddition of the acid load to the ultrafiltrate, which is reinserted inthe system upstream of the gaseous exchanger and ultrafiltrate.

It is also possible (as will be explained better in the followingdescription with reference to FIG. 4) to provide for a step of feedbackrecirculation of the blood flow, with inflow of an already ventilatedand further acidified blood flow portion coming from the patient, insuch a manner limiting the variation of the blood pH.

Further advantageously according to the invention, the method thenprovides for a step of removing the acid load from the treated blood.Considering that the organic acid part of the acid mixture (which in anycase should not exceed about 1 mMol/min, and thus can correspond in thecase of total removal from 10% to 30% of the total acid load) is removedby the treated patient's metabolism, in order to avoid a rapid acidosisof the patient, the removal step should involve the removal of thenon-metabolisable or inorganic acid load added to the blood.

In a preferred embodiment of the method according to the invention, theremoval step of the acid load of the treated blood, in particulardecarbonised blood, comprises a step of hydroelectrolytic rebalancing.Further advantageously, where the elimination of acid anions isaccompanied by a loss of cations, these are supplied to the patient,also in the form of bases (hydroxides).

It is possible to achieve, in a simple manner, such hydroelectrolyticrebalancing step of the treated blood by means of its directhaemodialysis before its reinsertion.

In this case, it is necessary to consider that, in particular in thecase of total or near-total removal of carbon dioxide, it is possible toreach very alkaline pH values, harmful for the red corpuscle, and whichcould cause calcium precipitation.

It is also possible to consider a step of removing the acid loadcomprising the steps of:

filtering the treated blood (in particular by means of a haemofilter)with obtainment of an ultrafiltrate (usually equal to 70-100 ml/min);

eliminating or discarding an ultrafiltrate amount such as to compensatefor the addition of the acid load, in particular eliminating acorresponding level of acid ions (CL-); and

subsequent infusion of a basic load amount in an appropriate region, inparticular a mixture of inorganic bases, including NaOH, KOH, Mg(OH)₂,Ca(OH)₂ and other positive ions, suitable for re-establishing thecontent of cations of the blood that have been lost with theultrafiltrate.

It can be immediately verified that the ultrafiltrate obtained from thetreated blood will have a load of anions (acids) of approximately 130mEq/liter and it is therefore possible to calculate the ultrafiltrateamount to eliminate in order to rebalance the acid content on the basisof the added acid load.

In particular, it is known that the blood ultrafiltrate has anelectrolytic content approximately equal to that of the plasma, withincrease of the anion content (Cl— and HCO3-) due to the lack of proteinin the ultrafiltrate phase. For example, if 5 mEq/minute of HCl acid areinfused (for a removal of between 50% and 100% of the carbon dioxideproduction) it will suffice eliminating between 40 and 50 ml/min ofultrafiltrate in order to maintain constant the bodily content of acidions (CL-). It is also necessary to infuse a basic load, in particular asolution which contains positive ions (Na, K, Mg and Ca) in hydroxideform, in order to maintain constant the concentration of these latter.

It should also be noted that this basic load infusion can appropriatelyoccur in a different path from that of the blood re-insertion, possiblyin a central vein.

The hydroelectrolytic rebalancing ultrafiltration can be carried outbefore or after the acidification step, if before eliminating also abicarbonate portion.

Alternatively, it is possible (and appropriate, above all if the totalremoval of carbon dioxide is carried out) to balance, directly orthrough dialysis, the ultrafiltrate according to one of the knownhydroelectrolytic rebalancing methods, including reverse osmosis,electrodialysis, passage on a column with basic ion exchange, diffusionor electro-dialysis through ion exchange membrane . . . (in the lattercase with acid recovery and possible reinfusion).

Moreover, the obtainment of an intermediate ultrafiltrate rather thanthe direct treatment of the blood is suggested by the need to preventthe blood from reaching very high pH values.

It is easily verified that the proposed method can effectively eliminatenearly all of the carbon dioxide content of the blood. It will sufficeto treat between 350 and 450 ml/min of blood in order to obtain a neartotal removal of the production/minute of carbon dioxide and thus permitthe substitution of the natural ventilation.

According to advantageous reaction variants, the blood treatment methodaccording to the invention comprises more than one step of acidifyingthe blood with insertion of several acid loads, so to eliminate greateramounts of carbon dioxide with chain transformations of the bloodbicarbonate into gaseous carbon dioxide. It is also possible to considerseveral blood ventilation steps.

The blood treatment method according to the invention can appropriatelycomprise pumping steps of the blood flow and/or ultrafiltrate.

The blood treatment method according to the invention is carried out bythe blood treatment device schematically illustrated in FIG. 1,generally indicated with 1.

In particular, the blood treatment device 1 comprises an inlet terminalIN for the inflow of a blood flow S and an outlet terminal OUT for theoutflow (i.e. return to the patient) of a treated blood flow St, inparticular with elimination of the carbon dioxide content and possiblyinsertion of oxygen.

Advantageously according to the invention, the blood treatment device 1comprises an acidification stage 2, a gas exchanger 3 and adeacidification stage 4.

More in detail, the blood flow S enters into the acidification stage 2,where it receives an acid load CA, transforming it into an acidifiedblood flow Sa that is inserted into the gas exchanger 3.

As seen above, the gas exchanger 3 is essentially a membrane oxygenatorthat eliminates the gaseous carbon dioxide content from the acidifiedblood flow (and possibly oxygenates it), giving rise to a decarbonisedand possibly oxygenated blood flow Sd, still acidified.

The decarbonised blood flow Sd is then inserted into the deacidificationstage 4 where the acid load present therein is eliminated with outflowof the treated blood flow St, such treated blood lacking carbon dioxideand the non-metabolisable portion of the acid load, and is then ready tobe re-inserted into the patient. In particular, in the deacidificationstage 4, it receives a basic load CB to add to the decarbonised bloodflow Sd exiting from the gas exchanger 3. Such base load can beappropriately infused in any other infusion line of the patient, so toavoid, depending on the use conditions, excessive pH changes of thetreated blood.

In a preferred embodiment of the invention, the blood treatment device 1also comprises a recirculation block 5 adapted to draw—in a feedbackpath—a portion Sf of the decarbonised blood flow Sd and mix it with theblood flow coming from the patient S before acidification in order tolimit sharp drops of the blood pH, as explained above with reference tothe blood treatment method according to the invention.

According to an alternative embodiment, the blood treatment device 1also comprises a haemofilter 6 for the ultrafiltrate production. Suchhaemofilter 6 is illustrated in FIG. 1 in dashed lines to show that itcan optionally be placed in different locations in the device, forexample, upstream of the acidification stage 2, or between theacidification stage 2 and the gas exchanger 3U, or downstream of the gasexchanger 3 before the deacidification stage 4, depending on thetreatment variants described above with reference to the methodaccording to the invention.

Of course, the blood treatment device 1 can be made with a series ofelements or blocks adapted to implement the different steps of themethod, as described above, separately optimised for carrying out thestep assigned to them, or by means of an integrated device suitable forachieving all the required blood treatment steps.

In FIG. 2, a first alternative embodiment of the blood treatment deviceis schematically illustrated, indicated with 1 a, suitable for making anacidification of an ultra filtrate recirculating through a membraneexchanger in veno-venous, or arterial-venous, or veno-arterial bypass.

In particular, the blood treatment device 1 a is connected to a patientPZ at a body vessel (connected to the inlet terminal IN of the device)and reinserted at the outlet terminal OUT of the device.

According to this first alternative embodiment, the blood is drainedfrom the patient PZ by a first pump P1 and crosses a gas exchanger 3, inparticular a membrane exchanger and then a haemofilter 6.

An ultrafiltrate Uf is thus obtained, which is acidified with an acidload CA, in particular with a mixture of physiological and inorganicacids, and reinserted in circulation upstream of the gas exchanger 3 bya second pump P2, which realises the circulation block 5. The bloodtreatment device 1 a therefore comprises a feedback path including thesecond pump P2 adapted to realise the recirculation block 5 of a portionof the ultrafiltrate Uf and the acidification stage 2, adapted to insertthe acid load CA into the drawn ultrafiltrate portion Uf.

A portion or level of ultrafiltrate UF is advantageously continuouslydiscarded, so to maintain the bodily acid content constant, the volumesubstituted with a solution of bases as described above. Thus, thehydroelectrolytic rebalancing step of the treated blood is achieved.

This first alternative embodiment of the blood treatment device 1 aaccording to the invention is particularly preferable in case of partialsubstitution of the natural ventilation function.

In FIG. 3, a second alternative embodiment of the blood treatment deviceis schematically illustrated, indicated with 1 b, adapted to achieve adirect acidification of the blood, a ventilation through a gaseousexchanger with subsequent stages and a final elimination of the acidload.

Also in this case, the blood treatment device 1 b is connected to apatient PZ at a body vessel (connected to the inlet terminal IN of thedevice) and reinserted at the outlet terminal OUT of the device.

According to this second alternative embodiment, the blood is drainedfrom the patient PZ by a first pump P1 and is acidified with a firstacid load CA at a first acidification stage 2 before being sent to afirst gas exchanger 3, in particular a membrane exchanger, where it isventilated.

The acidified and ventilated blood is then newly added with a secondacid load CA′ at a second acidification stage 2′, in such a mannerincreasing the carbon dioxide pressure. The blood is then newlyventilated by means of a second gas chamber 3′.

The number of acidification and gas exchange stages can be increased orreduced depending on the carbon dioxide removal needs.

The blood finally passes into a haemofilter 6 where a drawing ofultrafiltrate Uf occurs in order to achieve the hydroelectrolyticrebalancing step of the treated blood.

In FIG. 4, a third alternative embodiment of the blood treatment deviceis schematically illustrated, indicated with 1 c, suitable for achievingan acidification and a ventilation through a gaseous exchanger withblood recirculation.

Also in this case, the blood treatment device 1 c is connected to apatient PZ at a body vessel (connected to the inlet terminal IN of thedevice) and reinserted at the outlet terminal OUT of the device.

According to this third embodiment, the blood is drained from thepatient PZ by a first pump P1 and is recirculated at high flow into acircuit that comprises an acidification stage 2 for the inflow of theacid load CA and a gas exchanger 3 with blood recirculation achieved bya second pump P2 of the recirculation block 5 and final passage in thehaemofilter for the drawing of ultrafiltrate Uf adapted to achieve thehydroelectrolytic rebalancing step of the treated blood. The bloodtreatment device 1 c therefore comprises a feedback path including thesecond pump P2 adapted to realise the recirculation block 5 of a bloodflow portion and the acidification stage 2, adapted to insert the acidload CA into the drawn portion of the blood flow.

The advantage of this third alternative embodiment of the bloodtreatment device is the low resistance, at the expense of a highermechanical complexity (in particular with the need of two blood pumps).

In conclusion, advantageously according to the invention, the bloodtreatment method and device carry out an elimination of the relatedcarbon dioxide content such to permit a substitution of the naturalventilation, even if treating limited blood amounts.

In particular, the blood treatment method according to the inventionprovides for a continuous passage of blood in the treatment device (thisis therefore an extracorporeal treatment of the blood) and, byexploiting chemical-physical reaction mechanisms with an acid load, itachieves the transformation of the blood bicarbonate into gaseous formand permits its subsequent near-total elimination.

In substance, due to the liberation of the carbon dioxide contained inthe blood flow in blood bicarbonate form, it permits the treatment oflimited blood flows, in particular comparable to the blood flowsrequired for kidney dialysis treatment, with substantial improvement ofthe benefit-risk profile of the extracorporeal removal treatment of thecarbon dioxide. This technology can advantageously be applied to acuterespiratory insufficiency (known as ALI/ARDS, acronym of Acute LungInjury and Acute Respiratory Distress Syndrome, respectively), since itcan eliminate the need for mechanical ventilation and its dangers.Potential, important applications, with incalculable effects on theimprovement of the quality of life of the treated patients, can also beforeseen for those suffering from chronic respiratory insufficiency, orin any case for all the pathologies in which it is necessary toeliminate or reduce the ventilation need.

As indicated above, advantageously according to the invention, it ispossible to eliminate from the body the entire carbon dioxide amountproduced every minute, by treating even only 400-500 ml of blood (orother body fluid, the carbon dioxide content also being in any case highin the plasma or ultrafiltrate), instead of the 1.5 and 2.5 liters perminute of blood currently necessary for obtaining the objecting of theso-called “Total Co2 Removal”.

In other words, by using the method according to the invention, it ispossible to eliminate the need for mechanical ventilation, or even theneed to breath through the natural lungs, with a technology equippedwith an invasiveness and complexity entirely comparable to that of anormal haemodialysis.

Of course, the same advantage is obtained when only portions of thecarbon dioxide production/minute are to be eliminated. For example, withonly 200 ml of blood one eliminates about 50% of the carbon dioxideproduction, permitting to halve the natural ventilation need, in thecase of partial deficiency of the respiratory apparatus.

Of course, a man skilled in the art, in order to satisfy contingent andspecific needs, can make numerous modifications and variants to theabove-described blood treatment method and device, all comprised in theprotective scope of the invention as defined by the following claims.

The invention claimed is:
 1. A blood treatment device adapted to atleast partially eliminate the carbon dioxide content comprising: atleast one inlet terminal for inflow of a blood flow; an outlet terminalfor outflow of a treated blood flow; a circuit for blood flow definedbetween said at least one inlet terminal and said outlet terminal; atleast one acidification stage and one gas exchanger inserted, in serieswith each other, in said circuit between the inlet and outlet terminals,wherein said acidification stage is an infusion device adapted to insertan acid load in said blood flow, and said gas exchanger is adapted toventilate and eliminate the gaseous carbon dioxide content of saidacidified blood flow from said acidification stage; and adeacidification stage inserted downstream of said gas exchanger in saidcircuit; further comprising a haemofilter for the production ofultrafiltrate; wherein said haemofilter is connected in said circuitupstream of said acidification stage, said acid load being inserted insaid ultrafiltrate downstream of said haemofilter.
 2. The bloodtreatment device according to claim 1, wherein said gas exchanger is amembrane oxygenator adapted to eliminate, via pressure gradient, thegaseous carbon dioxide content from said acidified blood flow, givingrise to a decarbonized blood flow in said circuit upstream of saiddeacidification stage.
 3. The blood treatment device according to claim2, wherein said membrane oxygenator is adapted to oxygenate said bloodflow.
 4. The blood treatment device according to claim 2, wherein saiddeacidification stage is an infusion device adapted to add a basic loadto said decarbonized blood flow to remove said acid load by means ofanion elimination, thus obtaining a treated blood flow for supply tosaid outlet terminal.
 5. The blood treatment device according to claim1, further comprising a recirculation block adapted to draw, in afeedback path, a portion of said decarbonized blood flow downstream ofsaid gas exchanger and to mix it with said blood flow in order to limitthe blood pH variations upstream of said gas exchanger.
 6. The bloodtreatment device according to claim 1, wherein said haemofilter isconnected in said circuit upstream of said acidification stage, andwherein simultaneous loss of cations from said ultrafiltrate duringpassage of said blood flow through said acidification stage iscompensated for by means of an infusion of a suitable amount of cationsin hydroxide form into said blood flow.
 7. The blood treatment deviceaccording to claim 1, wherein said haemofilter is connected in saidcircuit between said acidification stage and said gas exchanger, saidgas exchanger being arranged to ventilate said ultrafiltrate downstreamof said haemofilter.
 8. The blood treatment device according to claim 1,wherein said haemofilter is connected in said circuit downstream of saidgas exchanger, said basic load being inserted by said deacidificationstage into said ultrafiltrate downstream of said haemofilter.
 9. Theblood treatment device according to claim 1, wherein said haemofilter isinserted into said feedback path in a recirculation block which mixes aportion of said ultrafiltrate with said acidified blood flow.
 10. Ablood treatment device adapted to at least partially eliminate thecarbon dioxide content comprising: at least one inlet terminal forinflow of a blood flow; an outlet terminal for outflow of a treatedblood flow; a circuit for blood flow defined between said at least oneinlet terminal and said outlet terminal; at least one acidificationstage and one gas exchanger inserted, in series with each other, in saidcircuit between the inlet and outlet terminals, wherein saidacidification stage is adapted to insert an acid load in said blood flowand said gas exchanger is adapted to ventilate and eliminate the gaseouscarbon dioxide content of said acidified blood flow from saidacidification stage; a deacidification stage inserted downstream of saidgas exchanger in said circuit; and a first pump for drawing said bloodflow and inserting into said gas exchanger and a haemofilter connectedin outlet with said gas exchanger as well as a feedback path for drawinga portion of said ultrafiltrate downstream of said haemofilter andreinserting the same upstream of said gas exchanger, said feedback pathcomprising a second pump adapted to make a recirculation block of saidportion of said ultrafiltrate and an acidification stage adapted toinsert an acid loadin said ultrafiltrate portion.
 11. The bloodtreatment device adapted to at least partially eliminate the carbondioxide content comprising: at least one inlet terminal for inflow of ablood flow; an outlet terminal for outflow of a treated blood flow; acircuit for blood flow defined between said at least one inlet terminaland said outlet terminal; at least one acidification stage and one gasexchanger inserted, in series with each other, in said circuit betweenthe inlet and outlet terminals, wherein said acidification stage isadapted to insert an acid load in said blood flow and said gas exchangeris adapted to ventilate and eliminate the gaseous carbon dioxide contentof said acidified blood flow from said acidification stage; adeacidification stage inserted downstream of said gas exchanger in saidcircuit; and a first pump for drawing said blood flow and inserting intoat least one gas exchanger, a plurality of acidification stages beingprovided for upstream of said at least one gas exchanger for the inflowinto said blood flow of a plurality of acid loads.
 12. The bloodtreatment device according to claim 11, wherein it comprises a pluralityof gas exchangers in cascade arrangement with each other, one of saidacidification stages being provided for upstream of each of said gasexchangers.
 13. A blood treatment device adapted to at least partiallyeliminate the carbon dioxide content comprising: at least one inletterminal for inflow of a blood flow; an outlet terminal for outflow of atreated blood flow; a circuit for blood flow defined between said atleast one inlet terminal and said outlet terminal; at least oneacidification stage and one gas exchanger inserted, in series with eachother, in said circuit between the inlet and outlet terminals, whereinsaid acidification stage is adapted to insert an acid load in said bloodflow and said gas exchanger is adapted to ventilate and eliminate thegaseous carbon dioxide content of said acidified blood flow from saidacidification stage; a deacidification stage inserted downstream of saidgas exchanger in said circuit; and a first pump for drawing said bloodflow and inserting into said gas exchanger and a haemofilter connectedin outlet to said gas exchanger as well as a feedback path for drawing aportion of said blood flow downstream of said gas exchanger andreinserting the same upstream of said gas exchanger, said feedback pathcomprising a second pump adapted to make a recirculation block of saidblood flow portion and an acidification stage adapted to introduce anacid load into said blood flow portion.